Folded-path cells for measuring optical absorption of gas-phase samples are well known in the art. Path lengthening, for increased analytical accuracy, is achieved therein through multiple reflection and traversal of the cell chamber by the analysis radiation beam.
In the so-called "White cell," which represents the seminal development in the field, the desired effect is produced by use of two side-by-side spherical objective mirrors arranged in confronting relationship to a third such mirror functioning as the field reflector (John U. White, "Long Optical Paths of Large Aperture", J. Opt. Soc. Am, No. 32 (1942), pp 285-288). A thermally stabilized long-path absorption cell of similar kind is described in Bragg et al, U.S. Pat. No. 4,749,276.
The demand remains however for a folded-path gas cell that enables further increases in effective path length, with more radiation throughput and less image blur. Such improvements would minimize energy losses and thereby serve to best preserve the resolution capability of associated optical instruments, as is essential for optimization of gas-phase quantitation.